Particulate polyolefin-liquid oxidizing agent propellant and rocket containing the same



United States Patent 3,136,669 PARTICULATE POLYOLEFIN-LIQUlD (DXIDIZINGAGENT PROPELLANT AND ROCKET CONTAIN- ING THE SAME l Richard A.Carpenter, Prairie Viilage, Kans., assigner to Spencer Chemical Company,Kansas City, Mo., a corporation of Missouri Filed Oct. 17, 1958, Ser.No. 767,946 6 Claims. (Cl. 149-74) This invention relates to propellantsand more particularly this invention is concerned with a monopropellantwhich may be utilized in uid form, and rockets utilizing themonopropellant.

Recent developments in space technology have resulted in an increaseddemand for new and improved rockets and propellants therefor. Rocketsare usually of two types, i.e., rockets with solid propellants androckets with liquid propellants.

In solid propellant rockets, the propellant charge contains all of thechemical elements for complete burning. The charge, which is usually amixture of solid fuel and solid oxidizer, is stored in the combustionchamber and upon ignition burns at a nearly constant rate forming thehot compressed gases which are accelerated and ejected at a highvelocity through a nozzle, imparting momentum to the system. However,there are several disadvantages with solid propellant rockets such asdiiculty of thrust vectoring, lack of combustion control such asthrottling or cutoff, and sometimes nonuniform distribution of theoxidizer throughout the fuel resulting in erratic burning.

In liquid propellant rockets, the propellant is usually a bipropellantsystem consisting of a liquid oxidizer and a liquid fuel which are fedunder pressure from separate tanks outside of the motor into the thrustchamber. The thrust chamber consists of a suitable combustion chamberwith one or more pairs of nozzles adapted to inject therein the fuel andoxidizer separately and simultaneously. The bipropellant reacts to formthe hot gases which are accelerated and ejected at a high velocitythrough the nozzle, providing momentum. This provides a system which canbe started, throttled and shut off at will, giving much better controlof thrust than is possible with solid propellants. However, the liquidbipropellant rocket propulsion system is highly complicated in design,requiring precision valves, pumps and complex feed mechanisms to supplythe combustion chamber with fuel and oxidizer at the optimum rate.

According to the present invention there is provided a novel rocketcontaining a novel, stable self-sufficient fluid monopropellant ofpre-determined composition, a cornbustion chamber with an exhaust gasdischarge nozzle and means for conveying the uid monopropellant to thecombustion chamber for burning therein to obtain thrust.

The novel uid monopropellant, which is one aspect of this invention,suitable for use in such a rocket comprises a stable fluid mixture of afinely divided polyolen resin intimately and uniformly dispersed andessentially suspended in a liquid oxidizer which has no appreciableadverse effect on the polyolefm at the temperatures encountered inmixing and storing the monopropellant.

The term uid used herein in regard to the monopropellant means trueliquids as Well as the more viscous liquids which are commonly referredto as gels and pastes and which have plasticV or rmoldable physicalcharacteristics. The term fluid thus includes substances havingparticles which easily move and change their relative position without aseparation of the mass, and which easily yield to pressure; capable ofowing, as defined by Websters New Collegiate Dictionary, based onWebsters New International Dictionary, 2nd Edition. However, the termfluid is lbroadly intended to mean that the monopropellant can be fedfrom a monopropellant reservoir in the rocket into the combustionchamber of a rocket by suitable means such as by gravity, pumps orthrough acceleration of the rocket itself once it is in flight.

The invention will now be described in conjunction with the attacheddrawing in which there is shown a rocket propelled by the novelmonopropellant herewith provided. This rocket is seen to contain arocket body l containing an enclosed tank 2, a combustion chamber 4,rocket thrust nozzle 14 communicating with the combustion chamber andpipe or conduit 8 for conveying iluid monopropellant 12 by means of pump10 and use of control valve 1l to the chamber 4 from tank 2. Space 3 isprovided between the base plate 6 of the fuel tank 4 and the insulatedtop 7 of the combustion chamber to provide protection against excessiveheat transfer to the fuel tank. Nozzle 9 is provided to spray themonopropellant into the combustion chamber to facilitate burning. Therocket is provided with stabilizing fins 13 which function as legs forthe rocket to' stand on for vertical firing. Electrical arc device 5 isprovided to tire the rocket although a pyrotechnic device may also beused for ring.

Although the rocket shown in the drawing is providedy with pump meansfor feeding the monopropellant to the s combustion chamber, a source ofcompressed gas may be alternatively employed to effect the feeding. Inaddition, once the rocket has been fired and is accelerating, the forceof acceleration and the inertia of the monopropellant should cause thefluid monopropellant to be fed into the combustion chamber.

Although not shown in the drawing, the stability of the monopropellantmakes it possible to circulate it around the combustion chamber as acooling liquid prior to its being fed into the chamber for burning.

Rockets employing the resinous polyolein-liquid oxidizer monopropellantsof this invention ignite at temperatures of about l200-l400 F. althoughthe temperature will vary with the oxidizer employed. Once ignition iseffected, however, the burning is self-sustaining.

The novel rocket of this invention utilizing such a fluid monopropellanthas all or nearly all of the advantages of rockets utilizing liquidbipropellants but is free of many of the disadvantages. Thus, themonopropellant rocket requires less than one-half of the plumbing neededin liquid bipropellant systems so that great weight reduction ispossible, reduced cost is achieved through the elimination of expensive`control devices, and the likelihood of breakdown or malfunction instorage or flight is accordingly reduced greatly. Because themonopropellant is stable and self-sucient, the rocket need contain onlya single fuel storage tank and a single set of feeding devices andcontrols for injecting the monopropellant into the combustion chamber.In addition, since the ingredient composition of the monopropellant ispredetermined, controls for varying the feed of a separate oxidizer anda seppropellants of this invention include liquid oxidizers such as redfuming nitric acid, white furning nitric acid, dinitro- 'The followingtable shows the required weight ratio of oxidizer to iinely dividedresinous polyolelin for propellants containing various oxidizers.V

gen tetraoxide and hydrogen peroxide. The oxidizers VTable l` should beliquid at the temperature of mixing andstorage, which-in some cases maybe below room tempera- Y Extent 0i Wirtin@ ture. In evaluating possibleliquid oxidizers, individual Oxidizer oxidation (odokproperties such asdensity, freezing point,v and cost are p y' considered as well as thecollective properties of the poly- RFNA Pam 3. olefin-oxidizer mixtures.In'the preferred embodiment of r C0mpiete 513 this invention, thevoxidizer is red fuming nitric acid WFNA2-- flllgete l (RFNA), which maybe described as concentrated nitric 100% H202-. L- Parmi """f 419 acidcontaining excess No2 (8-22% NO2). 9W H m i C g? r iete vii The resinouspolyoleiins which are suitable fuels in the 'Complete 8.1monopropellants are those derived by the polymerization N fete iig ofoleins, for example, polyethylene, polypropylene, poly- 1 butene-l andpolyisobutylene. Various grades of resinous ,.RFNA =re' fumng mmc acid(20% No polyolens are suitable; for example, with polyethylene, I zWri\1A=W1nteruiming nitric acid. have found that the lower densitymaterial as well as 20 1 medium density and high density resins may beemployed Of. collls?, ll. ls. ollVlollS the. fallos lllay belllgllel'0l' successfully i lower; however, .this will usually result inunreacted fuel Finely divided polyolens for use in the monopropelo l'oxldlzol Wltll' a 'le slllllllg, lowered ombllstloll eli lantsmay beprepared by several procedures such as ololloy: BloadlSf S PeaklllglloWoVofi from? t0 8 parts- .l precipitation, grinding or milling. Inpreparingmilled by Wolghl of OXldlZell may be combllled Wllh l Pall ofmaterial, the resin is milled or banburied at the fusionPoll/Olontemperature and then rapidly cooled while continuing the Thefollowing eX aI I1P1S s hOW the good mixture stability banburyingprocess until the finely divided material re- 0f Polyethylene-MIEI nllXtUfe-,S of fills mvolltlon- The, sults. In the precipitation process,the resin is dissolved general Prooodue of making thosomlxtufos Was asfol'l in a hot organic solvent, such as xylene, and allowed to loWS gel,and then a nonsolvent for the resin such as methanol A Sample of 3 gramsof -tllo llnoly'dlvlflod Polyethylene or water is added to precipitatethe finely divided poly- WaS Pl".lCe d lll a gladllaled 50llllcoll'fllfllge lube; YRed olefin fuming nitric acid (15.9 grams)having approximately The particle size of the polyoleiin in themonopropel- 20% Waslldedfo lll@ oelllllfllollbo aol the mlxf laut may befrom about l to about 500 microns. Howtule Sllllell Wllh a Sl-llllllgloll lllltll a SlulfYWas'ob'f ever, it has been found that whenpolyoleiins having `a talned- Thls gave o Welghl rollo of oXldlZol' loPolYothYlparticle sizeof about 50 to 150 microns are used the ro ene of53:1. An oil-sealed stirrer was theniitted in place sultant propellantVmixture is characterized by enhanced and the. mlxllll'e Slllled'atabout 500 r-P'lll' fol'llve lwlllsV mixture and excellent storagestability. That is, the rriix- 40 al room temperatur@ A The/Stlflolwas1111611 replaced Wlth.. Yture remains homogeneous and does not separateinto a Stopper and the lllllllul'e allowed lo Stand fol" lo llollls itwo components upon standingfor several days. at foomfompolatulo Theamount of fed fummg Dllflo The ratio of oxidizer to po1yo1en and thetype of acid which Yseparated out after standing was recorded. oxidizerused, determine the extent of oxidation of the Toomlxture Was thenoentflfogod. at .5QO f-P-Il- .fol' five' polyolom The optimum oxidizerto polyoleo Weight minutes and the amountof oxidizer which separated outratio for maximum specic impulse will generally lie with-V 'was agalllfoooldody in two levels, viz., that which gives partial oxidation (fuellll Several "l'lllls the Stlfflll' and oenlflfllgmg Profe.' rich): dureswere repeated one or two times to givetotal stirring (CHZ)+O2. C0 H2O 5periods of 10 and 15 hour'sand total 'standing times of 32 dvth t hi h l.d i hi t and 48 hours. 'The amount of oxidizer which had sepan a W cgives comp e e om a ou s 01C ome nc) arated out was recorded after each16 hour periodi (CH2)+1.5 O2 COM-H20 The following table gives theresults.l

Table Vi1 Oxidizer separated out Type of Particle Appar- Total f Total`Y poly- Method size of ent bulk stirring standing After standing Aftercentrifug- Run ethylenel of prep. PE (midensity time time ingY l (PE) ofPE 2 crous) of PE .(hrs.)V (hrs.)

(g-/ml j m1. Perm1, Percent cent P 50-100 0.24 5 i6 0.1` i 2.0 20` P f50-100 0.24 10 32 0. 0 o 2. 0 V20 P 50-100 0.24 15 64 0.0VV 0 2.0 20 P50 0.26 5 i6 0.1 1 2.0 P 50 0.26 i0` 32 0 0 1.5 Yi5 P 50 0. 26 15 04 0 01.3 13 P 50 Y0,20 5 is. 0.2 2 2.2 -22 M 20o-250 0. 41 5 16 0.5 5 4.5 45M 15o-20o 0. 39 5 16 0.3. 2 4.0 40 M 25o-300 0.35 5 16 4.0 40 4.8 k40 M50 0. 39 5 16 1.5 15 4. 5 45 P 50 0.32 5 16 0.5 5 4.0 y40 2 P=precipltated. M

The oxidizer (RFNA), although a liquid, is of higher density than thepolyoleiin, a solid, so that the small quantity of oxidizer whichseparates is at the bottom of the mixture. This is a feature which isadvantageous in rocket storage since plugging of outlet ports by a heavysolid at the bottom of a tank is avoided.

In a similar experiment with a N2O4-polyethylene mixture comprising a4.9:1 weight ratio of oxidizer to polyethylene, after standing 16 hoursat 10 C., none of the oxidizer had separated out and after centrifuging,0.8 ml. (8%) of the oxidizer had separated out.

The following examples demonstrate the good storage stability ofrepresentative oxidizer-polyethylene mixtures of this invention.

A 12 g. sample of finely divided polyethylene which had been prepared bymilling with a commercial Banbury mill and then screened to a particlesize of 5 0-100 microns (apparent bulk density of 0.38 g./ml.) wasprepared from a commercial, medium density (.935) polyethylene. Thepolyethylene was placed in a 125 ml. Erlenmeyer flask and 63.3 g. of redfuming nitric acid was added to the fiask to give anoxidizer-to-polyethylene weight ratio of 5.3:1. The flask was stopperedand the contents mixed by swirling until a slurry was obtained. Thestoppered flask was allowed to stand with daily swirling atapproximately room temperature. Samples were removed after 9 and 17 daysof standing. Each sample was diluted with a large volume of water andfiltered. The filter cake was washed with water until the filtrate wasneutral and the Washed polyethylene was triturated with ether, filteredand vacuum dried. The dried polyethylene was analyzed for nitrogencontent to determine the extent of chemical reaction with the oxidizer.After standing 9 days, the polyethylene had a nitrogen content of 0.30%and after standing 17 days there was found a nitrogen content of 0.32%.This indicates that there is very little chemical reaction between theoxidizer and the polyethylene at room temperature, thus, indicating themixture has very good storage stability characteristics.

Similar storage stability tests with RFNA-polyethylene andN201-polyethylene mixtures at 158 F. indicated good storage stabilityeven at this elevated temperature.

The propellants of this invention also have very good stability toignition or decomposition due to impact or compression as determined bypreliminary drop weight tests. This indicates that the propellants androckets containing the same may be safely handled by operating personnelwithout many of the safety precautions which are necessarily associatedwith many other propellants.

It has also been found that mixing the polyolefin and liquid oxidizerevolves no heat, thus providing a safer propellant system.

For an experiment to study the injection, ignition and burning ofRFNA-polyethylene mixtures, a simple hot tube reactor assembly wasassembled which was composed of the following parts:

(A) A fuel reservoir, fuel line and injector were constructed of a 1.5cm. I.D. x 20 cm. length of Pyrex tubing connected to a piece of 2 mm.I.D. Pyrex capillary tubing. The fuel was forced into the combustionchamber by means of nitrogen pressure,

(B) A combustion chamber was constructed of a 1.8 cm. I.D. x 36 cm.length of Vicor tubing. The tube was heated by means of a rheostatcontrolled combustion furnace (20 cm. long).

The fuel reservoir was filled with the propellant mixture and thenitrogen pressure line connected. The furnace was then heated to thedesired temperature and swept with nitrogen. The propellant mixtureswere injected by nitrogen pressure at the desired velocity and angle.Ignition and burning characteristics were noted and recorded. Thefollowing table gives the results.

Table Ill Reactor Run Type opolyethytube Ignition Type of burning N o.lene in mixture 1 temp. F.)

High density 1, 000 No Some sparking. do 1,200 Yes. Intermittent.

1, 200 Yes. Steady fire. 1, 470 Yes Few short flashes. 1,470 Yes- Do.1.470 Yes Sparks and short flashes. 1, 370 Yes Steady fire. 1,350 YesD0. 1,350 Yes Do.

1 RFNA (20%NO2)-polyethylene (particle size 50-100 microns) mixtureswith and oxidizer-to-fuel ratio of 53:1. The high density polyethylenehad a density of ,960, the medium density material had a density of.935, and the low density material had a density oi .918.

The results of this test show that ignition can be readily obtained atatmospheric pressure by employing a combustion chamber temperature inthe range of about 1200- 1400 F.

Although the examples are all with polyethylene, it is to be understoodthat other finely divided resinous polyolefns are also suitable as fuelsfor the propellants of this invention. Since they contain the sameelements, carbon and hydrogen, the oxidizer to fuel ratios would be thesame, dependent upon the oxidizer. Examples of other suitablepolyolefins would include polypropylene, polybutene-l, polyisobutylene,etc.

Obviously, various additives may also be employed in the propellantssystems of this invention, for example, to increase the heat ofcombustion or to modify the burning rate.

Various other changes and modifications of the invention can be madeand, to the extent that such variations incorporate the spirit of thisinvention, they are intended to be included within the scope of theappended claims.

What is claimed is:

1. A self-sufficient propellant consisting essentially of mixture offinely-divided polyethylene and fuming nitric acid, said mixture havinga Weight ratio of red fuming nitric acid to polyethylene ofapproximately 3.3 to 5.4 to 1, the finely-divided polyethylene having aparticle size of approximately 50 to 150 microns and said mixture as awhole taking the physical form of a liquid in which said finely-dividedpolyethylene is dispersed and which is susceptible of being fed inliquid form to a thrust chamber.

2. A self-sumcient fluid monopropellant consisting essentially of aratio of one part by weight of a finelydivided resinous polyolefinhaving a particle size of l to 500 microns dispersed in 3 to 8 parts byweight of a liquid oxidizing agent selected from the group consisting ofred fuming nitric acid, white fuming nitric acid, dinitrogen tetraoxideand hydrogen peroxide.

3. A self-sufficient uid monopropellant consisting essentially of aratio of one part by weight of a finelydivided resinous polyethylenehaving a particle size of 1 to 500 microns dispersed in 3 to 8 parts byweight of red fuming nitric acid.

4. A self-sufficient fluid monopropellant consisting essentially of aratio of one part by weight of a finelydivided resinous polyolefinhaving a particle size of 1 to 500 microns dispersed in 3 to l8 parts byweight of white fuming nitric acid.

5. A self-sufficient iiuid monopropellant consisting essentially of aratio of one part by weight of a finelydivided resinous polyolefinhaving a particle size of 1 to 500 microns dispersed in 3 to 8 parts byweight of dinitrogen tetraoxide.

6. A self-sufficient fluid monopropellant consisting essentially of aratio of one part by Weight of a finelydivided resinous polyolefinhaving a particle size of 1 to 500 microns dispersed in 3 to8 partsV byWeight of hy-V K OTHER REFERENCESV rdfogefl PefOXlde 'Moore et al.:JetPropulsion, V01. 26, No. 11, Novem- 'A ber 1956, pp. 965-8. f

References Cited inthe le of this patent Chemical and Engineering News,May 27,A 1957, 15p.

UNITED STATES PATENTS i Y v 5, 18-23. Y Y v 2,537,526 Hanuum Jam 9,1951V Zaehringer: lSolid Propellant Rockets, Second Stage,` 2,814,929Morley et aL 1)@ 3 1957 American Rocket Co., Boxl 1112, Wyandotte,Mich.,

FOREIGN PATENTS September 1958 PP 22%30" 582,621 l Greatritain VNov.22,19746 10 i

1. A SELF-SUFFICIENT PROPELLANT CONSISTING ESSENTIALLY OF MIXTURE OFFINELY-DIVIDED POLYETHYLENE AND FUMING NITRIC ACID, SAID MIXTURE HAVINGA WEIGHT RATIO OF RED FUMING NITRIC ACID TO POLYETHYLENE OFAPPROXIMATELY 3.3 TO 5.4 TO 1, THE FINELY-DIVIDED POLYETHYLENE HAVING APARTICLE SIZE OF APPROXIMATELY 50 TO 150 MICRONS AND SAID MIXTURE AS AWHOLE TAKING THE PHYSICAL FORM OF A LIQUID IN WHICH SAID FINELY-DIVIDEDPOLYETHYLENE IS DISPERSED AND WHICH IS SUCCEPTIBLE OF BEING FED INLIQUID FORM TO A THRUST CHAMBER.